1. Field of the Invention
The present invention relates to an annular hole cutters. More particularly, it relates to an annular hole cutter having alternating cutting teeth with different geometries.
2. Description of the Related Art
When annular hole cutters of this type are used, it is necessary to smoothly eject chips produced during cutting from the hole being drilled to reduce resistance to the cutting force. This requirement significantly affects the cutting performance of the annular cutter.
Many attempts have been made to improve the cutting performance. The annular hole cutter disclosed in Japanese Unexamined Utility Model Publication No. 57-177620 has a plurality of cutting teeth with sequential teeth having several different geometries. More specifically, as shown in FIGS. 23-26, the disclosed cutter includes four different types of cutting teeth. Some of the teeth, that is teeth 101 and 102, have pointed tips such that they have ridgeline style leading and lower edges. On the other hand, the leading edges of cutting teeth 103 and 104 include a flat or linear portion.
Another known annular hole cutter is disclosed in Japanese Unexamined Utility Model Publication No. 57-197411 and is shown in FIGS. 27 to 29. This cutter also uses ridgeline cutting teeth 105 and 106 together with linear edge cutting teeth 107 as shown in FIGS. 27 to 29. The combined use of different edge cutting teeth will produce chips of different shapes and sizes, so that the chips can be cut into pieces and be ejected smoothly.
In the annular cutters disclosed in both publications, however, the ridgeline cutting teeth and flat edge cutting teeth differ very much in angles and shapes of their bottom faces. This makes the production of these cutters and regrinding of the edges of the teeth troublesome. More specifically, in both producing cutters and regrinding the cutting edges after use, the bottom faces of the cutting teeth have to be ground. If the angles and shapes of the bottom faces vary from tooth to tooth, continuous grinding of the bottom faces is very difficult. A dresser is used for grinding these bottom faces in this case. With the bottom faces having the same angle, the angle of the dresser need not be altered and the dresser can continuously grind those faces.
As shown in FIG. 30, a ridgeline cutting tooth 34 whose cutting edge 31 has a crest 30 close to the center of the cutting edge 31 does not cut into a work piece 22 very well when a hole is to be drilled. In this case, chips are to be ejected in directions perpendicular to the cutting edge 31 as indicated by arrows in FIG. 30. If the cutting edge 31 takes a ridgeline shape, chips cut from opposite sides of the crest 30 will hit against each other above the cutting edge 31. Thus, they are not easily ejected from the hole. Consequently, the cutting edge 31 does not smoothly cut into the work piece 22. In some cases the cutting edge 31 may not properly cut in, so that the annular cutter binds on the work piece 22. This phenomenon is called "walking" in the related industry.
Other annular cutters as disclosed in Japanese Unexamined Patent Publication No. 59-93209, and U.S. Pat. Nos. 4,573,838, 4,586,857, 4,632,610, 4,813,819 and 4,952,102 have been proposed since the disclosure of the above-described types of cutters. Of these, the annular cutter disclosed in Japanese Unexamined Patent Publication No. 59-93209 is shown in FIGS. 31 and 32. Those proposed annular cutters basically use inner cutting teeth 37 each having a relief surface 38 and an outer cutting edge 39 separated inside and outside. With this structure, the annular cutters cut out narrow chips in such a way that the chips will not continuously follow one after another widthwise, thus ensuring smooth ejection of the chips. However, at least half of the teeth in these annular cutters have ridgeline relief surfaces.
It is noted, that the annular cutter disclosed in U.S. Pat. No. 4,952,102 has cutting teeth whose outer walls are slightly thinned. Therefor the crest of such cutting edges are shifted away from the center of the cutting edge. Regardless, the use of ridgeline cutting teeth will cause problems in that work efficiency is lowered when producing annular cutters and regrinding the cutting edges. Further, the cutting action of the teeth cutting into a work piece is poor at the beginning of the drilling.
Further, U.S. Pat. No. 4,952,102 indicates that even with the use of ridgeline cutting teeth, chips are ejected continuously in the widthwise direction. However, no consideration has been taken to form thick and very rigid chips. The annular cutter therefore provides relatively thin and soft chips. Additionally, if chips are cut into pieces to become narrower, the chips become easily entangled with one another due to their softness. Therefore, the chips will be entangled before being discharged from a drilled groove, which again, prevents smooth cutting.